Re: Destructor not called with forward declaration instead of include
On Apr 22, 4:43 am, internetpet <internet...@hotmail.com> wrote:
Say you have these files:
BigClazz.h
class Clazz; // Note the forward declaration only , no include
"Clazz.h"
class BigClazz
{
public:
BigClazz();
~BigClazz();
Clazz* pclazz;
};
BigClazz.cpp
#include "BigClazz.h"
BigClazz::BigClazz(){}
BigClazz::~BigClazz()
{
delete pclazz; // Here the destructor of of the Clazz object
will not be called
}
Clazz.h
class Clazz
{
public:
Clazz();
~Clazz();
};
Clazz.cpp
#include "Clazz.h"
Clazz::Clazz(){};
Clazz::~Clazz(){};
main.cpp
int main(int argc, char *argv[])
{
BigClazz* pVM = new BigClazz();
pVM->pclazz = new Clazz();
delete pVM;
}
If you run this you'll see that the Clazz destructor will not be
called when BigClazz does "delete pclazz;" in it's own destructor. But
if you replace the forward declaration in BigClazz (class Clazz;) with
an include
(#include "Clazz.h") then it works.
Any idea why?
Thanks
Eric
I believe this falls under "undefined behaviour". So it will depend on
the implementation, among other things.
From the standard 5.3.5:
"If the object being deleted has incomplete class type at the point of
deletion and the complete class has a
non-trivial destructor or a deallocation function, the behavior is
undefined."
Regards.
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